1. Field of the Invention
The present invention relates to a switch. More particularly, the present invention relates to a switch to which a pulsed high current is supplied.
2. Description of the Related Art
In a technique such as electromagnetic forming in which a metal material is plastically processed by utilizing an electromagnetic force, various kinds of forming is performed, for example, pipe expansion, flanging, pipe swaging, sheet metal forming, and so forth. In electromagnetic forming, an object of forming is positioned near an inductor, and energy charged in a capacitor is supplied as a pulsed high current to the inductor for an extremely short period of time of several milliseconds or shorter. Thus, magnetic flux is generated, and an induced current flows through the object of forming. Consequently, in accordance with the Fleming's left-hand rule, the object of forming is deformed plastically.
A gap switch as a pulsed current switch used in electromagnetic forming or the like is disclosed by Japanese Unexamined Patent Application Publication No. 2003-311434. In a gap switch, the discharging gap, i.e., the distance between electrodes, needs to be adjusted in accordance with conditions, such as humidity, of an ambient environment. Such circumstances increase the variation in the amount of deformation of the object of forming. Hence, the gap switch is not suitable for mass production.
In addition to the gap switch, Japanese Unexamined Patent Application Publication No. 2007-253182 proposes a thyratron switch, a semiconductor switch, and an ignitron switch as exemplary pulsed current switches. Among these switches, the ignitron switch is considered to be most suitable as a switch used in a mass production process in which discharge, i.e., shot, is caused for a number of times by supplying a pulsed high current to the switch.
Another option is a mechanical switch to which a current is supplied by mechanically bringing contact members into contact with each other. An exemplary mechanical switch applied to a case where a high current is used is disclosed by Japanese Unexamined Patent Application Publication No. 11-73848. In this mechanical switch, the materials of contact members have specific compositions, respectively, so that the adhesion, i.e., fusion, between the contact members is suppressed.
The degree of fusion may be reduced in the mechanical switch disclosed by Japanese Unexamined Patent Application Publication No. 11-73848. However, for example, in a case of a facility intended for mass production of electromagnetically formed products where discharge is caused successively for a number of times, the switch soon becomes unusable unless the occurrence of fusion is completely avoided, resulting in a reduction in the productivity and an increase in the cost.